1. Field of the Invention
The present invention relates to a flow control valve adopted to a refrigerating cycle, and more particularly, to a flow control valve in which a proportional control is enabled by employing a step motor, to thereby enhance flow control performance and durability.
2. Description of the Related Art
Generally, refrigerating cycles include an evaporator, a compressor, a condenser, and an expansion valve and so on, and serve to lower the ambient temperature by the evaporation, compression, condensation, and expansion of refrigerants.
In detail, the refrigerant liquid in the evaporator is evaporated, and the refrigerant liquid takes the heat required for such an evaporation from the air surrounding the cooling pipe. Then, the air is cooled down, which maintains the inside of the container at a low temperature by natural convection or a fan. The refrigerant liquid provided from the expansion valve and the vapour of the evaporated refrigerant coexist inside of the evaporator, and there is a certain relation between the evaporation pressure and the evaporation temperature during the liquid changes to the vapour.
The vapour of the refrigerant liquid is taken into the compressor, to thereby maintain a low pressure of the refrigerant in the evaporator. As a result, the refrigerant liquid can actively evaporate even at a low temperature. The vapour of the refrigerant taken into the compressor is compressed by a piston inside of a cylinder, thereby is provided with a high pressure. Thus, the vapour may be easily liquefied by a cooling water or a cooling air at the normal temperature.
The compressed gas from the compressor is cooled and liquefied by the condenser. Similar to the evaporation described above, the refrigerant liquid and the vapour of the refrigerant liquid coexist and there is a certain relation between the condensation pressure and the condensation temperature during the vapour changes to the liquid.
An expansion is for lowering the pressure of the refrigerant which is liquefied by the condenser, to be easily evaporated prior to the submittal of the refrigerant to the evaporator. The expansion valve reduces the pressure and controls the amount of the refrigerant liquid.
That is, the amount of the refrigerant liquid to be evaporated in the evaporator is determined by the amount of the heat to be removed in the container at a predetermined evaporation temperature (pressure). Therefore, it is extremely significant to precisely provide and control the amount of the refrigerant liquid in the evaporator.
The expansion valve adiabatically expands the refrigerant liquid at a high temperature and pressure to a low temperature and pressure by throttling, and serves as a flow control valve for maintaining an appropriate amount of refrigerant according to the load of the evaporator.
Expansion valves may be classified into various types according to the operating method and structure. Of recent interest is, the thermocompression type flow control valve which costs less, has an excellent driving force, and for which a fine driving is enabled. An example of such a thermocompression type flow control valve will be explained with reference to the attached drawings.
As shown in FIG. 1, the flow control valve includes a cap 1, a plate 3 which is made up of a ceramic and has dilatant liquid injection openings 2, an aluminum(Al) electrode 5 which has at the medial portion thereof a tantalum(Ta)--Al heating electrode 4 so as to fixed onto the heating plate 3, a diaphram 7 which is made up of a copper(Cu), for example, and which is fixed onto Al electrode 5 with a spacer 6 inserted therebetween, adhesive layers (also referred to as "fillers") 8 and 9 which are inserted between the upper surface of Al electrode 5 and the bottom surface of spacer 6, and the upper surface of spacer 6 and the bottom surface of diaphram 7, respectively, so as to enhance an adhesion, a dilatant liquid 10 which fills the space between Al electrode 5 and diaphram 7, and sealing bottom plate 11 which is fixed at the bottom surface of plate 3 so as to close dilatant liquid injection openings 2.
Reference numeral 12 denotes a power supply line.
Cap 1 has a space portion 1a through which the refrigerant liquid flows, and a liquid inlet passageway 1b and a liquid outlet passageway 1c which communicate with space portion 1a.
In constructing such a thermocompression type flow control valve, Al electrode 5 having Ta--Al heating electrode 4 is fixed onto plate 3, and adhesive layer 8, spacer 6, adhesive layer 9, and diaphram 7 are sequentially fixed onto Al electrode 5, to thereby form a predetermined space within Al electrode 5, spacer 6, and diaphram 7, respectively.
Subsequently, dilatant liquid 10 is injected via dilatant liquid injection openings 2, and sealing bottom plate 11 is fixed to the bottom surface of plate 3 so as to close dilatant liquid injection openings 2. Then, sealing bottom plate 11 is fixed to the bottom surface of cap 1, and power supply line 12 of Al electrode 5 is led out toward the outside of cap 1.
Here, diaphram 7 has to be positioned in such a manner that the center portion thereof is positioned directly under liquid outlet passageway 1c of cap 1.
In such a conventional flow control valve, the refrigerant liquid flows in via liquid inlet passageway 1b, passes through space portion 1a, and flows out toward the evaporator via liquid outlet passageway 1c. When it is necessary to control the quantity of the refrigerant liquid, a power is applied to Al electrode 5 via power supply line 12, and Ta--Al heating electrode 4 of Al electrode 5 emits a heat. Then, dilatant liquid 10 which fills Al electrode 5, spacer 6, and diaphram 7 expands. As a result, as shown in FIG. 2, diaphram 7 expands at the center thereof toward liquid outlet passageway 1c of cap 1. Ultimately, the quantity of the refrigerant liquid which flows out via liquid outlet passageway 1c is controlled, to thereby control an overall liquid flow.
However, in such a conventional thermocompression pressure type flow control valve, the quantity of the liquid is controlled by expanding dilatant liquid 10 by heating Ta--Al heating electrode 4, and a proportional control is not allowed. In addition, there some disadvantages to overcome due to the use of dilatant liquid 10.
In other words, a seal to completely prevent leakages of dilatant liquid 10 is not easily, and a low durability of diaphram 7 is caused by the repeated expansion and contraction of dilatant liquid 10. As a result, reliability of the flow control valve is degraded, and an overall lifespan of the valve is reduced.